This invention relates to fan blade assemblies and in particular, to a more efficient fan assembly and a method of making the same.
Whenever natural ventilation is unsuitable, as for example in large office blocks, industrial buildings, or where toxic fumes or harmful dusts are released, mechanical ventilation is necessary. The fans employed, conventionally are driven by electric motors, are broadly classified according to their action on the air, as axial or centrifugal fans. Axial fans cause air to move substantially parallel to the axis of the fan. A fan assembly typically consists of an annular hub, a hub plate or spider having arms attached to the hub and fan blades secured to arms of the spider. The hub in turn is attached to a shaft which is connected with two pulleys and a belt to the motor. The fan blades are typically secured to the spider arms by rivets. The main characteristic of axial flow fans is that for a given power output from a driving motor, they can handle large volumes of air, especially when flow is relatively unobstructive. When, however, there is resistance to air flow, recirculation or backward flow may occur through the fan itself, owing to the inablility of slower moving parts of the blades close to the hub to equal the pressure caused nearer the blade tips were circumferential speed is the greatest. Such resistance can be caused, for example, by filters, heaters, or long or circuitious runs of ducting. In these kinds of applications, the operating conditions produce large shear and tension forces which eventually cause the rivets holding the fan blades to the spider arms to wear out. Blade detachment destroys fan operability. Repair is difficult in many applications and generally expensive to accomplish.
By studying the effect of the parameters which effect fan performance, an efficient fan can be designed. These parameters include blade shape, number of blades, and spacing between the blade and the fan hub and between the blade and the fans associated venturi. It is known that fan efficiencies increase if the fan blade is curved. However, when a curve is put into the blade, the blades often spring back, especially if made from a metal. In other words, the blade recovers some of its original shape after being formed in a die. This is especially true where cost is a consideration. That is, efficient blade designs are well known in the art. Their construction, however, are expensive. Our invention permits a manufacture to make, in a high production, low cost environment , a highly efficient, relatively low cost fan.